Yea it stands for 4mm, they didn't carry them at Rona or Home Depot so I had to go to a store that specalized in fasteners. The one I went to was called Fasten-all. If you look in the yellowpages under screws or fasteners I'm sure you'll be able to find a store that carries them.

FYI, Fastenal has these M4 screws to fit Black Ice rads. My local store has to bring them in from their distribution, and I have to buy a minimum of $10 worth, and I have to wait until Friday. Still cheaper than buying a new rad.